1. Field of the Invention
The present invention relates to a key telephone system in which a dial number is transmitted and received between a main unit and an extension telephone apparatus by a peculiar control signal.
2. Related Background Art
Hitherto, in the key telephone system (KTS), an extension telephone converts the input dial number, into a control signal of a predetermined format and sends the signal to an extension circuit in a main unit.
In the main unit, the dial number received by the extension circuit is transmitted by a trunk circuit in a form of a dial pulse or a PB signal in accordance with the contract with a telephone company.
On the other hand, portable electronic apparatuses which can store and read out various information (additional valuable information such as schedule, telephone number, address, etc.) for use at any time have been put into practical use as manufactured articles. Among such apparatuses, there is also an apparatus (automatic dialer) in which by indicating a registered telephone number, a PB signal of the indicated telephone number can be generated as a sound from an audio output unit such as a speaker or the like. Therefore, by speech transmitting the generated PB signal from a mouthpiece of the telephone to the line, the telephone number can be dialed to the distant partner side. In association with the wide spread of electronic apparatuses having such an auto-dialing function, users' demand for the ability, even in the extension telephone of the KTS, to use the auto-dialing function in a manner similar to a common, ordinary telephone has become stronger and stronger.
However, in the above conventional apparatus, since the dialed number is transmitted and received between the extension telephone and the main unit by means of a control signal which is peculiar to the KTS, there is the problem that it is impossible to call by using an electronic apparatus which transmits the dial number by oscillating a PB signal.